How to name organic compounds

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How to name organic compounds

How to name organic compounds

It is no longer new that if you are writing JAMB, you will definitely come across questions that will instruct you to name certain organic compounds, such questions do give students headache as most students find it hard to properly name organic compounds.
How nice would it be if you can correctly name organic compounds, even if you know it before, this article will expose you to more hints and tricks to name organic compounds.

  • What you’re going to learn in this article
  • What are parent names!
  • How do we choose the correct chain?
  • How do we identify substituents?
  • How do we start numbering? (From left or right?)
  • How do we name compounds?

What are parent names?

Parent names are simply functional groups, in a particular compound, the first thing is to identify the parent name, I will advise you to carefully study functional groups, for example if you see ‘OH’ in any compound, you will easily know that the parent name is alkanol, here are few functional groups

  1. OH (Alkanol)
  2. Single bond (alkane)
  3. Double bond (alkene)
  4. Triple bond (alkyne)
  5. -COOH (Alkanoic)
  6. -CHO (Alkanal)
  7. -O- (Ether/Alkoxyalkane)
  8. -COO- (Ester/Alkanoates) etc.

Please study the rest carefully, they are very important, so in any compounds given to you, what do you need to identify first?, yes! Good! Parent names!

How do we choose the correct chain?

What are chains?, definition of catenation will answer this;

Catenation is the ability of carbon to combine together to form chains (straight, branch or cyclic chains)

Here it should be noted that carbon bond to carbon to form chains, so bonding of carbon to carbon is what we call chains.
Before you can name any compound, after identifying the parent name, you need to identify the longest chain, chains can be in different forms, some chains might be ‘U’ shape, some might be ‘Π’ shape, you need to understand how long the carbon bond to one another, always select longest chain first.
So after selecting longest chain, the number of carbon in the longest chain will be the parent name, I.e assuming you’ve gotten the functional group in the parent name as Alkanol, and in the longest chain the number of carbon is 8, then your parent name will be what???, yes! Octanol.
Don’t forget the counting mono (1), di (2), tri/prop (3), tetra (4), penta (5), hexa (6), hepta (7), octa (8) Nona (9) and deca (10). They are not more than this for O’ level students.

How do we identify Substituents?

Substituents in organic chemistry means any elements or compounds that substitute (replace) hydrogen in an organic compound, the main substituents are halogens such as bromine, fluorine, chlorine and iodine, and also all alkyl group such as methyl (CH3), ethyl (C2H5), propyl (C3H7) etc. So whenever you see any of the above elements or compounds in an organic compound, just know that they are substituents.

How do we start numbering?

The mistake most students make is by misquoting New School Chemistry, majority of the students believe numbering starts from left and left alone, but this is wrong!, you can start numbering from either left or right, it just depends on you to know where to start numbering from, you will learn the technique in this article.
First take your numbering from the left, write the positions of substituents on the carbons down somewhere then add them together, take your numbering from the right also and write down the positions of substituents on the carbons, sum it and compare it with what you first got, the smallest one is the one you will go with, here is an example:

  • FROM THE LEFT: There are substituents on carbon 2, carbon 4 and carbon 5(2+4+5=11)
  • FROM THE RIGHT: There are substituents on carbon 1, carbon 3 and carbon 5 (1+3+5=9)

Now compare the two sum gotten, 9 is smaller than 11, therefore the numbering will start from the RIGHT! (please always go with the sum with lowest priority)

How do we name compounds?

Nice, to name compounds in organic chemistry, you need to identify the parent name, choose the longest chain, identify the substituents, and their locations, know where to start numbering from, but in addition to this, there are some hints that you need to take care of.

  1. While arranging the substituents, always arrange halogens (chlorine, fluorine, iodine, bromine) before any akyl group, also while arranging them, arrange the halogens in alphabetical order, followed by the akyls and also arrange them in alphabetical order
  2. If a substituent appears on multiple carbons, use prefix such as di (2), tri (3) etc
  3. Separate letters and figures with hyphen (-) and figures and figures with comma (,)
  4. If there is double bond or triple bond or any functional groups apart from single bond in a compound, there is need for you to specify the position of the functional group, I will cover this in my next article, your comments will motivate me to write it though.

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